1. Field of the Invention
The present invention pertains to a mechanical crawling device that may be capable of motion over diverse and complex topographies. In particular, this invention pertains to a mechanical crawler that moves via an out-of-plane wave driven in its foot.
2. Discussion Of Related Art
An active area of research in the field of robotics and mechanical engineering, is locomotion. There is an increasing need for machines that are capable of self-propelled motion in a variety of complex and challenging topographies.
For example, downhole tractors are used in the oil and gas industry to convey equipment, such as logging equipment, within a borehole. These downhole tractors are required to operate in the difficult environment of the borehole, and may be required to traverse a variety of soil/formation consistencies and boreholes of varying diameters and profiles. One example of a downhole tractor that may be used in boreholes is described in WO 2005/008023. This tractor uses a continuous track rotatably disposed about idler wheels, for locomotion, similar to tank tracks. The tractor also includes an actuator arm or link assembly (see U.S. Pat. No. 6,910,533, entitled “Mechanism that Assists Tractoring on Uniform and Non-Uniform Surfaces” issued to Schlumberger Technology Corporation on Jun. 28, 2005, incorporated by reference herein in its entirety) that can move the track assembly outward and inward to adapt to varying hole diameters.
Robotic design frequently looks to biology to gain insight into the mechanics of locomotion. In particular, adhesive locomotion, used by most marine and terrestrial gastropods (e.g., snails) is inspiring a new paradigm in robotics. Adhesive locomotion offers several advantages. First, gastropods have only one foot so they are mechanically simple and very stable. Second, gastropods are often found in habitats that are topologically complex and thus have evolved means of maneuvering through challenging terrains, for example, by adhering to the substrate which they are traversing. These advantages make robotic replication attractive.
Observations of crawling snails have allowed biologists to learn that the muscles along the foot of the snail drive deformations that propel the animal forward. The moving foot is divided into alternating bands of translating waves and interwaves, where waves correspond to regions of lateral compression in the foot. The waves have been classified as direct waves (propagating in the direction of the animal's movement in this case a snail) and retrograde waves (propagating in a direction opposite to the snail's movement). Differential friction between the foot and the ground in the wave and interwave segments is required to move the snail forward. As the snail propels itself forward, the forces created by muscles in the foot interact with the substrate (i.e., the surface across which the snail is moving) through a layer of mucus secreted by the snail, known as the pedal mucus. Locomotion is directly coupled to the stresses generated within this layer of mucus and is dependent on the dynamic and material properties of the mucus. It has been found that the requisite differential friction arises naturally if the applied stresses in the interwave region remain below the critical yield stress (such that the mucus acts as an adhesive), while stresses in the wave region are sufficient to create a flow in the mucus, propelling the snail forward in a “caterpillar-like” motion.
The advantages of gastropod locomotion, coupled with developments in material science and soft actuators, has lead to the design of some mechanical snails. For example, a paper by Ito et al. entitled “Film Structured Soft Actuator for Biomimetics of Snail's Gastropod Locomotion published at the 6th International Conference Control, Automation, Robotics and Vision ICARCV'2000 (2000), describes a mechanical snail comprised of a series of electromagnets beneath a soft matrix. A layer of viscous fluid (emulating the pedal mucus) is deposited on a soft surface and a rigid snail is placed on top of the fluid. The electromagnets are activated in sequence, creating an out-of-plane wave in the surface, which propels the mechanical snail. However, this design is not ideal as it is not the snail that generates the waves, but rather by the surface. Thus locomotion is dependent on and driven by the surface and the snail is not self-propelled.
Another example of a mechanical crawling device is described in a paper by Mahadevan et al. entitled “Biomimetic Ratcheting Motion of a Soft, Slender, Sessile Gel,” published in PNAS 101(1), 23 (2004), which uses soft hydrogel crawlers to investigate crawling movements. In this example, forward motion is produced by differential friction that is supplied by angled incisions in the gel. Thus, like Ito's design, it is the substrate that provides propulsive energy, and the snail is not self-propelled.